What must you do after attaching a semitrailer?

The selected combination of answers is correct because both of those steps are critical according to German traffic regulations for ensuring the safety and functionality of a semitrailer.

1. Checking the fastening and locking system of the fifth wheel is essential to ensure that the connection between the tractor unit and the semitrailer is secure, preventing any detachment while driving.

2. Connecting and checking all hoses and cables is crucial for the proper functioning of braking systems and electrical connections. If any of these are not correctly connected or are faulty, it could lead to serious safety risks.

By completing both of these tasks, drivers help ensure that the semitrailer is safe to operate on the road, adhering to the principles outlined in the German Road Traffic Act (StVG) and related regulations. Missing any of these steps could result in legal consequences and increased risks on the road.